Page 331 - Multidimensional Chromatography

Industrial and Polymer Applications 321

that are not completely resolved, or not resolved at all, when using a single GC
column.
The determination of trace impurities in various major industrial materials such
as gasoline, styrene and aniline by using a combination of programmed-temperature
sample introduction, mass-flow-controlled multi-column dual-oven capillary gas
chromatography and on-line mass spectrometry has been demonstrated (20). The
cryotrapping at the inlet of the second column resulted in significant improvement in
the resolution of critical peak pairs and reproducibility of the analysis. The multi-
column analysis of aniline was performed by using an OV-17 (25 m 0.32 mm i.d.,
d f
1.0 m precolumn (Figure 12.14(a)) and an HP(1– 50 m 0.32 mm i.d.,
d f
1.05 m) second column. The shaded compound (peak) is solvent flushed via a
splitline to permit detection by mass spectrometry of impurities in the aniline and
also to prevent overloading of the MS detector. The analysis of aniline was carried
out both with (Figure12.14(c)) and without cryotrapping (Figure 12.14(b)), where it
is found that the use of cryotrapping leads to increased resolution between the
phenol and aniline present in the sample.
Another example of multi-column analysis has been demonstrated for the deter-
mination of impurities in styrene. The marked compounds in the styrene sample
(Figure 12.15(a)) were solvent flushed via a splitline, with the analysis being carried
out with a cryotrapping separation (CTS) (see Figure 12.15(b)). The first column,
was an Ultra-2 (25 m 0.32 mm i.d., d f
0.25 m) precolumn, while the main col-
umn was a DB-WAX (30 m 0.32 mm, d f
0.25 m) with an FID being employed
as the detection system.
This multi-column swithching (GC–GC) technique has also been shown to be a
powerful method for the separation of benzene and 1-methyl-cyclopentane in
gasoline, as well as for the analysis of m-and p-xylenes in ethylbenzene.

Figure 12.14 Chromatographic analysis of aniline: (a) Precolumn chromatogram (the com-
pound represented by the shaded peak is solvent flushed); (b) main column chromatogram
without cryotrapping; (c) main column chromatogram with cryotrapping. Conditions: DCS,
two columns and two ovens, with and without cryotrapping facilities: columns OV-17
(25 m 0.32 mm i.d., 1.0 m d.f.) and HP-1 (50 m 0.32 mm, 1.05 m d f ). Peak identifica-
tion is as follows: 1, benzene; 2, cyclohexane; 3, cyclohexylamine; 4, cyclohexanol; 5, phenol;
6, aniline; 7, toluidine; 8, nitrobenzene; 9, dicyclohexylamine. Reprinted with permission
from Ref. (20).